Avalanche photodiode

Abstract

To provide an avalanche photodiode capable of lessening concentration of an electric field and also reducing parasitic capacitance.SOLUTION: There is provided an avalanche photodiode that comprises a first mesa with a light reception region, a first electrode provided at the first mesa, a second mesa connected to the first mesa, and a pad provided at the second mesa and electrically connected to the first electrode, and a connection part where the first mesa and second mesa are connected has a plane shape which is curved inward convexly.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present disclosure relates to avalanche photodiodes. [Background technology]

[0002] Avalanche photodiodes are known as light-receiving elements that detect optical signals. An electrode is provided on the mesa of the light-receiving element. A pad for wire bonding is connected to the electrode (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-108852 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-328036 Summary of the Invention [Problem to be solved by the invention]

[0004] If the wiring connecting the electrode and mesa is provided along the mesa, there is a risk of the wiring being broken due to the step of the mesa. Therefore, by providing the pad on the mesa as well, it is placed at the same height as the electrode. However, edges are created in the semiconductor layer, and there is a risk of electric field concentration at the edges. Furthermore, as the mesa becomes larger, parasitic capacitance increases. Therefore, the objective is to provide an avalanche photodiode that can alleviate electric field concentration and reduce parasitic capacitance. [Means for solving the problem]

[0005] The avalanche photodiode according to the present disclosure comprises a first mesa having a light receiving region, a first electrode provided on the first mesa, a second mesa connected to the first mesa, and a pad provided on the second mesa and electrically connected to the first electrode, and the planar shape of the connection portion where the first mesa and the second mesa are connected is an inwardly convex curve. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide an avalanche photodiode that can alleviate the concentration of an electric field and reduce parasitic capacitance. [Brief explanation of the drawings]

[0007] [Figure 1A] FIG. 1A is a plan view illustrating an avalanche photodiode according to the first embodiment. [Figure 1B] FIG. 1B is a plan view illustrating the mesa of the avalanche photodiode according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating an avalanche photodiode. [Figure 3A] FIG. 3A is a cross-sectional view illustrating a method for manufacturing an avalanche photodiode. [Figure 3B] FIG. 3B is a cross-sectional view illustrating a method for manufacturing an avalanche photodiode. [Figure 3C] FIG. 3C is a cross-sectional view illustrating a method for manufacturing an avalanche photodiode. [Figure 4] FIG. 4 is a plan view showing an example of mounting an avalanche photodiode. [Figure 5A] FIG. 5A is a plan view illustrating a mesa of an avalanche photodiode according to Comparative Example 1. FIG. [Figure 5B] FIG. 5B is a plan view illustrating the mesa of the avalanche photodiode according to Comparative Example 2. As shown in FIG. [Figure 6] FIG. 6 is a plan view illustrating a mesa of the avalanche photodiode according to the second embodiment. [Figure 7] FIG. 7 is a plan view illustrating the mesa of the avalanche photodiode according to the third embodiment. [Figure 8] FIG. 8 is a plan view illustrating the mesa of the avalanche photodiode according to the fourth embodiment. [Figure 9]FIG. 9 is a plan view illustrating the mesa of the avalanche photodiode according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0009] One aspect of the present disclosure is an avalanche photodiode (1) comprising a first mesa having a light-receiving region, a first electrode provided on the first mesa, a second mesa connected to the first mesa, and a pad provided on the second mesa and electrically connected to the first electrode, wherein the planar shape of the connection portion where the first mesa and the second mesa are connected is an inwardly convex curve. The curved connection portion can alleviate electric field concentration. The reduction in the total area of ​​the first mesa, second mesa, and connection portion can reduce parasitic capacitance. (2) In the above (1), the planar shape of the connection portion may include an arc that contacts an end of the first mesa and an end of the second mesa, thereby alleviating electric field concentration and reducing parasitic capacitance. (3) In the above (2), the planar shape of the first mesa and the planar shape of the second mesa may include a circle, and the diameter of the arc of the connecting portion may be equal to or smaller than the diameter of the first mesa and equal to or smaller than the diameter of the second mesa. This can alleviate electric field concentration and reduce parasitic capacitance. (4) In the above (3), the diameter of the arc of the connecting portion may be 10 μm or more, and may be equal to or less than the diameter of the first mesa and the diameter of the second mesa. This can alleviate electric field concentration and reduce parasitic capacitance. (5) In any one of (1) to (4) above, the first mesa and the second mesa may form an 8-shape in plan view. This can alleviate electric field concentration and reduce parasitic capacitance. (6) In any of the above (1) to (5), the first electrode may be ring-shaped, the light-receiving area may be located inside the first electrode, and the pad may be located outside the first electrode. By widening the light-receiving area, the amount of light that can be received increases, improving sensitivity. (7) In any one of (1) to (5) above, the first electrode may be ring-shaped, the light-receiving region may be located inside the first electrode, and the pad may protrude inside the ring shape of the first electrode. Wire bonding to the pad can be performed stably. (8) In any one of (1) to (4) above, the second mesa may have an extension extending in a direction away from the first mesa, and the connection portion may connect the first mesa and the extension. This can alleviate electric field concentration and reduce parasitic capacitance. (9) In any one of the above (1) to (8), the first electrode may have a curved shape that follows the connection portion. This reduces electrical resistance and enables stable wire bonding. (10) In any one of (1) to (9) above, the device may include a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type, a light absorption layer and a multiplication layer provided between the first semiconductor layer and the second semiconductor layer, and a second electrode electrically connected to the first semiconductor layer, wherein the first mesa and the second mesa include the second semiconductor layer, the light absorption layer, and the multiplication layer, and the first electrode is electrically connected to the second semiconductor layer. This can reduce parasitic capacitance generated between the first semiconductor layer and the second semiconductor layer.

[0010] [Details of the embodiments of the present disclosure] Specific examples of avalanche photodiodes according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0011] First Embodiment Fig. 1A is a plan view illustrating an avalanche photodiode 100 according to the first embodiment. Fig. 1B is a plan view illustrating a mesa 10 of the avalanche photodiode 100. Fig. 2 is a cross-sectional view illustrating the avalanche photodiode 100, showing a cross section taken along line AA in Fig. 1A.

[0012] As shown in FIG. 1A, the avalanche photodiode 100 has a mesa 10. The mesa 10 has a mesa 12 (first mesa), a mesa 14 (second mesa), and a connection portion 16. A substrate 30 (first semiconductor layer) extends from a position overlapping the mesa 10 to the outside of the mesa 10. The top surface of the substrate 30 is parallel to the XY plane. Two sides of the substrate 30 are parallel to the X axis. The other two sides are parallel to the Y axis. The Z axis direction is the thickness direction of the substrate 30. The mesa 10 protrudes in the Z axis direction beyond the top surface of the substrate 30. The X axis, Y axis, and Z axis directions are perpendicular to one another.

[0013] 1A and 1B, the planar shapes of mesa 12 and mesa 14 in the XY plane include circles. Circular mesa 12 and circular mesa 14 are connected to each other at two connection portions 16. In the XY plane, mesa 12 and mesa 14 form the shape of an Arabic figure eight. The diameter of mesa 12 is D1. The diameter of mesa 14 is D2. The diameter D1 of mesa 12 is larger than the diameter D2 of mesa 14. The area of ​​mesa 10 is the sum of the areas of mesa 12, mesa 14, and connection portion 16.

[0014] An electrode 22 (first electrode) is provided on the mesa 12. A pad 24 is provided on the mesa 14. The electrode 22 has a circular planar shape and is provided on the outer periphery of the mesa 12. The portion of the mesa 12 inside the electrode 22 becomes the light-receiving region 18. The pad 24 has a circular planar shape and is located outside the electrode 22 and in contact with the electrode 22. The electrode 20 (second electrode) is spaced apart from the mesa 10 and is provided on the substrate 30. The electrode 20 has a circular planar shape. The electrode 20 also functions as a pad, and is connected to, for example, a bonding wire.

[0015] 2, the avalanche photodiode 100 has a substrate 30 (first semiconductor layer), a multiplication layer 32, a light absorption layer 34, and a semiconductor layer 36 (second semiconductor layer). In the Z-axis direction, the multiplication layer 32, the light absorption layer 34, and the semiconductor layer 36 are stacked in this order on one surface of the substrate 30. The multiplication layer 32, the light absorption layer 34, and the semiconductor layer 36 are provided in an area narrower than the substrate 30, and form a mesa 10.

[0016] The substrate 30 is a semiconductor substrate and is formed of, for example, n-type indium phosphide (n-InP). The multiplication layer 32 is formed of, for example, undoped indium phosphide (i-InP). The light absorption layer 34 is formed of, for example, indium gallium arsenide (InGaAs). The semiconductor layer 36 includes, for example, a p-type indium phosphide (p-InP) layer and a p-type indium gallium arsenide (p-InGaAs) layer. The semiconductor layers of the avalanche photodiode 100 may be formed of compound semiconductors other than those mentioned above. For example, electric field relaxation layers may be provided between the light absorption layer 34 and the multiplication layer 32 and between the light absorption layer 34 and the semiconductor layer 36.

[0017] The insulating film 38 is a passivation film that covers the upper surface of the substrate 30 and the side and upper surfaces of the mesa 10. The insulating film 38 is made of an insulator such as silicon nitride (SiN), silicon oxide (SiO2), or silicon oxynitride (SiON). The insulating film 38 has an opening above the mesa 10 and also has an opening at a position away from the mesa 10.

[0018] The electrode 20 is spaced apart from the mesa 10, provided in an opening in the insulating film 38, and electrically connected to the substrate 30. The electrode 22 and the pad 24 are provided on the mesa 10 and electrically connected to the semiconductor layer 36. The electrode 20, the electrode 22, and the pad 24 are made of metal.

[0019] 1B is an imaginary circle that is located outside mesas 12 and 14 and is tangent to the ends of mesas 12 and 14. Diameter D3 of circle C is equal to or smaller than diameter D1 of mesa 12 and equal to or smaller than diameter D2 of mesa 14. In the XY plane, the planar shape of connection portion 16 is an inwardly convex curve and includes the arc of circle C. That is, connection portion 16 includes the arcs tangent to the ends of mesas 12 and 14.

[0020] (Manufacturing method) 3A to 3C are cross-sectional views illustrating a method for manufacturing the avalanche photodiode 100. As shown in Fig. 3A, a multiplication layer 32, a light absorption layer 34, and a semiconductor layer 36 are epitaxially grown in this order on the upper surface of a substrate 30 by, for example, metal organic chemical vapor deposition (MOCVD).

[0021] 3B, the semiconductor layer 36, the light absorption layer 34, and the multiplication layer 32 are etched to expose the upper surface of the substrate 30. The mesa 10 is formed in the portion that was not etched.

[0022] As shown in FIG. 3C, an insulating film 38 is formed by, for example, plasma enhanced chemical vapor deposition (PECVD). Openings are formed in the insulating film 38 at positions spaced apart from the mesa 10 and in a portion covering the top surface of the mesa 10. The electrodes 20, 22, and pads 24 are formed by vacuum deposition and lift-off. The avalanche photodiode 100 is formed through the above steps.

[0023] 4 is a plan view showing an example of mounting an avalanche photodiode 100. The avalanche photodiode 100 is placed on the surface of a substrate 40. An electrode 20 of the avalanche photodiode 100 is electrically connected to an electrode 42 of the substrate 40 by a bonding wire 46. A pad 24 of the avalanche photodiode 100 is electrically connected to an electrode 44 of the substrate 40 by a bonding wire 48. The substrate 40 can be sealed with a cap or the like to form a package such as a CAN package.

[0024] (Comparative Example 1) 5A is a plan view illustrating the mesa 10 of the avalanche photodiode according to Comparative Example 1. The connection portion 13 between the mesas 12 and 14 has a shape that conforms to the electrode 22 and the pad 24, and includes an edge that protrudes inward. Since an electric field concentrates at the edge-shaped connection portion 13, there is a high possibility that an edge breakdown will occur.

[0025] (Comparative Example 2) 5B is a plan view illustrating the mesa 10 of the avalanche photodiode according to Comparative Example 2. The connection portion 15 between the mesas 12 and 14 has a shape that connects a tangent line of the mesa 12 and a tangent line of the mesa 14. Because the connection portion 15 does not have an edge shape, the concentration of the electric field is alleviated. However, because the area of ​​the mesa 10 is larger than that of Comparative Example 1, the parasitic capacitance increases.

[0026] According to the first embodiment, the mesa 12 is provided with a light-receiving region 18. The mesa 12 and the mesa 14 are connected at a connection portion 16. As shown in FIGS. 1A and 1B, the connection portion 16 has an inwardly convex curve. Because the connection portion 16 does not have an edge shape, the concentration of the electric field can be alleviated. Edge breakdown is less likely to occur. Compared to Comparative Example 2, the area of ​​the mesa 10 is smaller, so the parasitic capacitance can be reduced.

[0027] As shown in FIG. 1B, circle C contacts the end of mesa 12 and the end of mesa 14. The planar shape of connection portion 16 includes the arc of circle C and has no edges. This makes it difficult for an electric field to concentrate at connection portion 16. Since a high voltage of, for example, several tens of volts or even about 100 volts is applied to the avalanche photodiode 100, the electric field strength becomes high. According to the first embodiment, it is possible to mitigate electric field concentration when a high voltage is applied.

[0028] The planar shape of mesa 12 includes a circle with a diameter D1. The planar shape of mesa 14 includes a circle with a diameter D2. Diameters D1 and D2 are, for example, several tens of micrometers to several hundreds of micrometers. Diameter D3 of the arc of connecting portion 16 is equal to or smaller than diameter D1 of mesa 12 and equal to or smaller than diameter D2 of mesa 14. In the example of FIG. 1B, diameter D1 of mesa 12 is larger than diameter D2 of mesa 14. Diameter D3 of connecting portion 16 may be equal to or smaller than diameter D2 of mesa 14. The area of ​​mesa 10 is reduced, thereby reducing parasitic capacitance.

[0029] The smaller the diameter D3 of the connection portion 16, the smaller the area of ​​the mesa 10, reducing the parasitic capacitance. On the other hand, the smaller the diameter D3, the sharper the shape of the connection portion 16, which may result in electric field concentration. To mitigate electric field concentration, the diameter D3 of the connection portion 16 is set to 10 μm or more. That is, the diameter D3 is 10 μm or more and is equal to or smaller than the diameter D1 of the mesa 12 and the diameter D2 of the mesa 14. The connection portion 16 has no edges, and the area of ​​the mesa 10 is reduced. This makes it possible to achieve both electric field concentration reduction and reduced parasitic capacitance. The lower limit of the diameter D3 may be 10 μm, or may be 5 μm, 15 μm, 20 μm, etc.

[0030] Mesas 12 and 14 are circular in plan view, forming a figure-8 shape. The ends of mesas 12 and 14 have no edges in the XY plane, but are curved, making it difficult for electric fields to concentrate. The planar shape of mesas 12 and 14 is a closed curve, such as a circle or ellipse, and does not have a vertex.

[0031] 2, the avalanche photodiode 100 has an n-type semiconductor substrate 30, a multiplication layer 32, a light absorption layer 34, and a p-type semiconductor layer 36. Parasitic capacitance occurs between the substrate 30 and the semiconductor layer 36. According to the first embodiment, the area of ​​the mesa 10 is reduced, thereby reducing the parasitic capacitance.

[0032] The electrode 22 is provided on the mesa 12 and has a circular ring shape. A light-receiving area 18 can be provided on the mesa 12 inside the electrode 22. Because the electrode 22 is circular, the light-receiving area 18 is circular. Increasing the light-receiving area 18 increases the amount of light that can be received, improving sensitivity. However, it is difficult to connect a bonding wire to the circular electrode 22. The pad 24 is connected to the electrode 22 and is located outside the circular electrode 22. By connecting a bonding wire to the pad 24, the bonding wire and the electrode 22 can be electrically connected.

[0033] The electrode 22 may have any ring shape, such as a circular ring, an elliptical ring, or a closed curve. The portion of the mesa 12 surrounded by the electrode 22 functions as the light-receiving region 18. This allows connection between the electrode 22 and the semiconductor layer 36 and increases the amount of incident light.

[0034] Second Embodiment FIG. 6 is a plan view illustrating the mesa 10 of the avalanche photodiode according to the second embodiment. The same configuration as in the first embodiment will not be described. As shown in FIG. 6, the diameter D2 of the mesa 14 is larger than the diameter D1 of the mesa 12. The connection portion 16 is an inwardly convex curve and has no edges. The connection portion 16 includes an arc tangent to the mesas 12 and 14. The diameter of the arc is equal to or smaller than the diameter D1 of the mesa 12.

[0035] According to the second embodiment, the concentration of the electric field can be alleviated because the connection portion 16 does not have an edge shape. The area of ​​the mesa 10 is reduced, so the parasitic capacitance can be reduced.

[0036] <Third embodiment> 7 is a plan view illustrating the mesa 10 of the avalanche photodiode according to the third embodiment. Description of the same configuration as in the first or second embodiment will be omitted.

[0037] As shown in FIG. 7, similarly to the first embodiment, the mesa 12 is circular. The mesa 14 has an extending portion 14a and a curved portion 14b. The extending portion 14a is, for example, linear and protrudes away from the mesa 12 in the Y-axis direction. The curved portion 14b is provided at a position opposite the extending portion 14a from the mesa 12. The curved portion 14b is, for example, arc-shaped, or semicircular. The electrode 22 is annular and follows the outer periphery of the mesa 12. The pad 24 has a shape that follows the mesa 14, has a linear extending portion and an arc-shaped portion, and is located outside the electrode 22.

[0038] According to the third embodiment, the connection portion 16 is connected to the mesa 12 and the extension portion 14a of the mesa 14, and has an inwardly convex curve. Because the connection portion 16 does not have an edge shape, it is possible to alleviate the concentration of the electric field. Compared to an example in which the connection portion is formed by joining a tangent to the mesa 12 and a tangent to the curved portion 14b of the mesa 14, the area of ​​the mesa 10 is smaller, which reduces the parasitic capacitance.

[0039] <Fourth embodiment> 8 is a plan view illustrating the mesa 10 of the avalanche photodiode according to the fourth embodiment. Description of the same configuration as in the first to third embodiments will be omitted.

[0040] As shown in FIG. 8, the planar shape of mesa 12 is circular. Mesa 14 is provided midway around mesa 12. Connection portion 16 between mesa 12 and mesa 14 has an inwardly convex curved shape. Electrode 22 has a circular planar shape. Pad 24 has a circular planar shape. Pad 24 protrudes inside the circular shape of electrode 22. Light-receiving region 18 is not a perfect circle, but has a shape with a portion missing, such as a crescent shape.

[0041] According to the fourth embodiment, the connection portion 16 does not have an edge shape, so that the concentration of the electric field can be alleviated. The mesa 14 is smaller, so that the area of ​​the mesa 10 is further reduced. The parasitic capacitance can be reduced.

[0042] Fifth Embodiment FIG. 9 is a plan view illustrating a mesa 10 of an avalanche photodiode according to the fifth embodiment. Descriptions of the same configurations as those of any of the first to fourth embodiments will be omitted. As shown in FIG. 9, mesas 12 and 14 are circular, as in the first embodiment, and form a figure-8 shape. Mesa 12 is larger than mesa 14. Connection portion 16 is an inwardly convex curve and has no edges. Connection portion 16 includes an arc tangent to mesas 12 and 14. Electrode 22 has a curved shape that conforms to connection portion 16.

[0043] According to the fifth embodiment, the connection portion 16 does not have an edge shape, so the concentration of the electric field can be alleviated. The area of ​​the mesa 10 is reduced, so the parasitic capacitance can be reduced. The electrode 22 in FIG. 7 is larger than the example in FIG. 1B, so the electrical resistance is reduced. Wire bonding can also be performed stably.

[0044] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present disclosure as described in the claims. [Explanation of symbols]

[0045] Mesas 10, 12, and 14 13, 15, 16 Connection parts 14a Extension part 14b Curved section 18 Light receiving area 20, 22, 42, 44 electrodes 24 pads 30, 40 board 32 Multiplication layer 34 Light absorbing layer 36 Semiconductor layer 38 insulating film 46, 48 Bonding wire 100 Avalanche Photodiode

Claims

1. a first mesa having a light receiving region; a first electrode provided on the first mesa; a second mesa connected to the first mesa; a pad provided on the second mesa and electrically connected to the first electrode; The avalanche photodiode has a connecting portion where the first mesa and the second mesa are connected, and the planar shape of the connecting portion is an inwardly convex curve.

2. 2. The avalanche photodiode according to claim 1, wherein the planar shape of the connection portion includes an arc tangent to an end of the first mesa and an end of the second mesa.

3. the planar shape of the first mesa and the planar shape of the second mesa include a circle; 3. The avalanche photodiode according to claim 2, wherein the diameter of the arc of the connecting portion is equal to or smaller than the diameter of the first mesa and equal to or smaller than the diameter of the second mesa.

4. 4. The avalanche photodiode according to claim 3, wherein the diameter of the arc of the connecting portion is 10 [mu]m or more, and is equal to or less than the diameter of the first mesa and the diameter of the second mesa.

5. 3. The avalanche photodiode according to claim 1, wherein the first mesa and the second mesa form an eight-shaped configuration in plan view.

6. the first electrode is ring-shaped; The light receiving region is located inside the first electrode, 3. The avalanche photodiode according to claim 1, wherein the pad is located outside the first electrode.

7. the first electrode is ring-shaped; The light receiving region is located inside the first electrode, 3. The avalanche photodiode according to claim 1, wherein the pad protrudes to the inside of the ring-shaped first electrode.

8. the second mesa has an extension extending in a direction away from the first mesa, 3. The avalanche photodiode according to claim 1, wherein the connecting portion connects the first mesa and the extending portion.

9. 3. The avalanche photodiode according to claim 1, wherein the first electrode has a curved shape that follows the connecting portion.

10. a first semiconductor layer having a first conductivity type; a second semiconductor layer having a second conductivity type; a light absorption layer and a light multiplication layer provided between the first semiconductor layer and the second semiconductor layer; a second electrode electrically connected to the first semiconductor layer, the first mesa and the second mesa include the second semiconductor layer, the light absorption layer, and the multiplication layer; 3. The avalanche photodiode according to claim 1, wherein the first electrode is electrically connected to the second semiconductor layer.

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